1. Field of the Invention
Embodiments of the present invention relate in general to novel methods useful in the treatment of alcohol dependence or alcohol abuse. Embodiments of the present invention also relate to novel assay systems useful in initial screening of compounds having an antidipsotropic effect. Such compounds are useful in therapeutic methods of reducing alcohol consumption as a treatment for alcohol dependence or alcohol abuse.
2. Description of Related Art
Alcohol abuse and alcohol dependence (i.e., alcoholism) are serious public health problems of modern society. In the United States alone, an estimated 13 million adults exhibit symptoms of alcohol dependence due to excessive alcohol intake, and an additional 7 million abuse alcohol without showing symptoms of dependence according to U.S. Government projections from studies conducted in the mid-1980s. Alcohol dependence and abuse are very expensive: in economic and medical terms, it will cost the U.S. well over $200 billion in 1991 with no prospect of falling or leveling off. The social and psychological damages inflicted on individuals as a consequence of alcohol abuse, e.g., children born with fetal alcohol syndrome (FAS) and victims of alcohol-related accidental death, homicide, suicide, etc., are immense.
While it is generally accepted that alcoholism and alcohol abuse are afflictions with staggering international economic, social, medical, and psychological repercussions, success in preventing or otherwise ameliorating the consequences of these problems has been an elusive goal. Only very recently the public view that alcoholism and alcohol abuse are remediable solely by moral imperatives has been changed to include an awareness of alcoholism and alcohol abuse as physiological aberrations whose etiology may be understood and for which therapy may be found through scientific pursuits. Both alcohol abuse and dependence arise as a result of different, complex, and as yet incompletely understood processes. At present, alcohol research is in the mainstream of scientific efforts.
Our studies on alcohol (ethanol or ethyl alcohol) have been based on the hypothesis that its abuse can ultimately be understood and dealt with at the molecular level. Such a molecular understanding, if achieved, would provide a basis for the identification and development of appropriate therapeutic agents, as well as assay systems useful in screening compounds as antidipsotropic agents.
Daidzin is the major active principle in extracts of Radix puerariae, a traditional Chinese medication that suppresses the ethanol intake of Syrian golden hamsters. See Keung, W. M. and Vallee, B. L. (1993) Proc. Natl. Acad. Sci. USA 90, 10008-10012 and Keung, W. M., Klyosov, A. A., and Vallee, B. L. (1997) Proc. Natl. Acad. Sci. USA 94, 1675-1679 each hereby incorporated by reference in its entirety for all purposes. It is the first isoflavone recognized to have this effect and to be useful in therapeutic methods of reducing alcohol consumption. See U.S. Pat. No. 5,624,910 hereby incorporate hereby incorporated by reference in its entirety for all purposes. Daidzin is also a potent and selective inhibitor of human mitochondrial aldehyde dehydrogenase (ALDH-2 also known as ALDH-I) which is an enzyme involved in the major enzymatic pathway responsible for ethanol metabolism in humans. See Keung, W. M. & Vallee, B. L. (1993) Proc. Natl. Acad. Sci. USA 90:1247-1251. See also, U.S. Pat. No. 5,204,369 hereby incorporated by reference in its entirety for all purposes.
The ethanol intake suppressive activity ("antidipsotropic activity") of daidzin has also been confirmed in Wistar rats, Fawn hooded rats, and the genetically bred P rats under various experimental conditions, including two-lever choice (ethanol/starch), two-bottle free-choice (ethanol/water), limited access, and ethanol deprived paradigms. See Keung, W. M. & Vallee, B. L. (1994) EXS 71, 1254-1260; Heyman, G. M., Keung, W. M. & Vallee, B. L. (1996) Alcohol. Clin. Exp. Res. 20, 1083-1087; Overstreet, D. H., Lee, Y. W., Rezvani, A. H., Pei, Y. H., Criswell, H. E. & Janowsky, D. S. (1996) Alcohol. Clin. Exp. Res. 20, 221-227; Overstreet, D. H., Rezvani, A. H. & Lee, Y. W. (1996) Alcohol. Clin. Exp. Res. 20 16A; Lin, R. C., Guthrie, S., Xie, C.-Y., Mai, K., Lee, D. Y., Lumeng, L. & Li, T.-K. (1996) Alcohol. Clin. Exp. Res. 20, 659-663. These laboratory findings identify or confirm daidzin or one or more of its derivatives, analogs and/or metabolites as important compounds in the treatment of alcohol abuse and/or alcoholism.
It has been postulated that the accumulation of biogenic amines, such as serotonin and dopamine, coupled with the inhibition of the enzyme aldehyde dehydrogenase (ALDH) leads to an accumulation of biologically active biogenic aldehydes or active condensation products of biogenic amines and aldehydes, such as tetrahydroisoquinolines and beta carbolines, and that these products may affect drinking behavior. See Dietrich, R. A. and Erwin, V. (1980) Annu. Rev. Pharmacol. Toxicol. 20, 55-80. In addition, studies have been suggested to identify pharmacological agents that may depress the desire to drink by directly interfering with the neurotransmitters serotonin, dopamine, and .gamma.-aminobutyric acid (GABA) such as serotonin reuptake inhibitors, dopamine agonists, GABA receptor agonists, and narcotic antagonists. Numerous serotonin reuptake inhibitors, such as zimelidine, citalpram, viqualine, and fluvoxamine, are asserted to be effective in reducing alcohol consumption in animals. See Lawrin, M. O., Naranjo, C. A., and Sellers, E. M. (1986) Psychopharmacology Bulletin 22, 1020-1025. These compounds, however, react directly with the neurotransmitter.
It has also been postulated that ALDH-2 is somehow involved in the oxidation of aldehydes that derive from biologically active monoamines such as serotonin and dopamine in mammalian brain tissue via the action of monoamine oxidase. Axelrod, J., Kopin, I. J., and Mann, J. D. (1959) Biochim. Biophys. Acta. 36, 576-585 and Erwin, V. G. and Deitrich, R. A. (1966) J. Biol. Chem. 241, 3533-3539. Studies on dopamine metabolism in isolated mitochondria and various subcellular fractions identified ALDH-2 as the principal enzyme that catalyzes the oxidation of dopamine derived 3,4-dihydroxyphenylacetaldehyde (DOPAL) in rat liver. Tank, A. W., Weiner, H. And Thurman, J. A. (1981) Biochem. Pharmacol. 30, 3265-3275. Recent kinetic analyses have shown that both DOPAL and serotonin-derived 5-hydroxyindole-3-acetaldehyde (5-HIAL) are substrates for ALDH-2. Ambroziak, W. And Pietruszko, R. (1991) J. Biol. Chem. 266, 13011-13018.
However, the art has not recognized whether isoflavone based compounds such as daidzin or daidzin analogs are capable of interacting with the enzyme systems of neurotransmitters or how such compounds would even come in contact with such enzyme systems given the nature and structure of the isoflavone based compounds. As such, the art provides no guidance as to whether isoflavone based compounds are chemically capable of interacting with the neurotransmitter enzyme systems, such as where crossing of the blood-brain barrier may be necessary or are capable of having any effect on neurotransmitter enzyme systems, especially in a manner to reduce alcohol consumption or otherwise affect the concentration or efficacy of substrates within the enzyme system that regulate ethanol drinking behavior. A complete understanding of whether daidzin interacts with neurotransmitter enzyme systems to suppress ethanol intake is, therefore, necessary and beneficial. Such a further and complete understanding of the mechanism of action of daidzin's antidipsotropic activity and its interaction with neurotransmitter enzyme systems will identify other compounds useful as antidipsotropic agents, as well as provide novel assay systems to screen compounds for antidipsotropic activity.